When police asked for the password to unlock his phone, Syed said: "Yeah, I.S.I.S. You like that?"

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File photo of London, United Kingdom. A British teen has plead guilty to planning a terror attack in the city.

A British teenager accused of planning a bombing in London pleaded guilty Thursday to preparing terrorist acts.

Prosecutors say Haroon Syed tried to buy weapons and explosives online from an extremist named "Abu Yusuf." The contact was actually a series of British intelligence agents.

The 19-year-old told his contact he needed a machine gun and an explosive vest so he could "after some damage with machine gun do martyrdom."

He said he was considering targeting London's busy Oxford Street and searched online for potential locations, including an Elton John concert in Hyde Park on Sept. 11, 2016 — the 15th anniversary of the 9/11 attacks.

Syed was arrested Sept 8. When police asked for the password to unlock his phone, Syed said: "Yeah, I.S.I.S. You like that?"

Syed's elder brother, Nadir Syed, was sentenced last year to a minimum of 15 years in prison for plotting an Islamic State-group-inspired beheading to coincide with Remembrance Sunday war commemorations.

Defense lawyers claimed Haroon Syed was a vulnerable young man who was groomed by radicals online but never intended to carry out an attack.

His lawyer, Mark Summers, had asked for the case to be thrown out, saying authorities should have enrolled Syed in a counter-radicalization program "to steer him away from the path it was feared he was going down, rather than guiding him down it."

Judge Michael Topolski refused to throw out the case, and Syed pleaded guilty at London's Central Criminal Court. He will be sentenced June 8.